This invention relates to a system for controlling the activation of an air bag for use in a vehicle.
An air bag is mounted on that portion of a vehicle opposed to the passenger of the vehicle. Upon crash or collision of the vehicle, a squib of the air bag is fired or activated to produce gas in the air bag to instantaneously expand or inflate the air bag, thereby protecting the passenger.
A system for activating a squib of such an air bag, as disclosed in Japanese Laid-Open (Kokai) Patent Application No. 247147/88, includes an energy-reserving capacitor connected to a battery via a relatively long electric wire. A switch (first switching means) is connected between one terminal of the capacitor connected to the battery and the squib of the air bag. This switch has the function (first control means) for detecting deceleration of the vehicle, and upon collision of the vehicle, this switch detects an abrupt deceleration of the vehicle and is closed, so that the switch allows electric current from the battery to flow to the squib to activate the same. Even if the electric wire is broken or cut when the vehicle collision takes place, the electric charge stored up in the capacitor is supplied to the squib, thus effecting the activation of the squib without fail.
In the system of the above Japanese Laid-Open application, when the electric wire or a fuse connected to the electric wire is cut, an alarm lamp (malfunction alarm device) is lit to tell the drive of the vehicle of this fact. More specifically, this alarm lamp is connected to the terminal of the capacitor connected to the battery, and also is grounded via a transistor. The cutting of the electric wire is detected by a monitor circuit (second control means), and the transistor is turned on in response to a detection signal from the monitor circuit, thereby lighting the alarm lamp. The supply of electric current to the alarm lamp is effected by discharging the electric charge stored up in the capacitor, since because of the cutting of the electric wire, electric current can not be supplied from the power source (battery).
In the activating control system of the above Japanese Laid-Open application, when the electric wire is cut, the electric charge stored up in the capacitor is much or completely consumed after the alarm lamp is lit for a long time, which results in a problem that the squib of the air bag fails to be activated upon collision of the vehicle.
Other prior art includes Japanese Laid-Open Patent Application Nos. 241231/86, 166636/88 (corresponding to U.S. Pat. No. 4,887,843) and 164649/89. Laid-Open Application No. 241231/86 discloses a control system provided with an energy-reserving capacitor. Laid-Open Application No. 166636/88 discloses a control system in which an energy-reserving capacitor is charged by a battery via an inductance. Laid-Open Application No. 164649/89 discloses a control system provided with a microcomputer.